Parenteral amino acid formulations for the inhibition of systemic hypotension associated with nitric oxide production

ABSTRACT

An anti-hypotensive formulation comprising an essentially arginine-free or low arginine (less than about 0.1%, most preferably, about 0.01%) containing mixture of amino acids is provided. The invention in particular embodiments of the anti-hypotensive formulation includes ornithine, citrulline or both. A method for prophylaxis and treatment of systemic hypotension in an animal is provided. Most particularly, a method for treating hypotension caused by nitric oxide synthesis through administering a low or essentially arginine-free parenteral formulation to an animal, so as to reduce or eliminate nitric oxide synthesis is described. A method for treating an animal in septic shock is also disclosed, comprising administering to the animal an anti-hypotensive formulation comprising a mixture of amino acids, which is essentially arginine free.

Work relating to the development of the present invention was supportedat least in part by the National Institute of Health Grant No. DK-37116.Therefore, the Federal Government may have certain rights to use of thisinvention.

This is a divisional of application Ser. No. 07/767,265 filed Sep. 27,1991 now U.S. Pat. No. 5,286,739.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of prophylaxis and treatmentof hypotension. Most particularly, the present invention proposesmethods for the control and inhibition of hypotension or systemic shockthrough the administration of particularly defined formulations withlimited nitric oxide-generating potential. The present invention alsorelates to specially tailored nutritional formulations for patients atrisk of hypotension or systemic shock which include low concentrationsof arginine or are arginine-free. Particular embodiments of theformulations also include ornithine or citrulline as urea cyclesubstrates. Anti-hypotensive TPN formulations for the generalnutritional support of patients are also provided as within the scope ofthe present invention.

2. Background of the Art

Hypotension, or low blood pressure, is a complicating and oftenlife-threatening condition attendant to shock, traumatic injury, sepsis,the administration of immunomodulators, as well as other situations.Thus, the risk of hypotension affects a significant number of personsthroughout the world. For example, septic shock, a life-threateningcomplication of bacterial infections, affects 150,000 to 300,000patients annually in the United States alone.¹

The cardiovascular collapse and multiple metabolic derangementsassociated with septic shock are due largely to bacterial endotoxin(ET), which has been shown to elicit a septic shock-like condition whenadministered to animals². ET is known to stimulate the synthesis andrelease of several cytokines and biological mediators having hypotensiveactivity; among the factors released, TNF, platelet activating factor(PAF), prostacyclin and complement-derived C5a anaphylatoxin have beenproposed as contributors to the cardiovascular collapse of septicshock³⁻⁶.

Although it has been shown that animals pretreated with anti-TNFantibodies⁷, PAF receptor antagonists⁸, and prostacyclin synthesisinhibitors⁹ are significantly protected against septic shock, therelative importance of these mediators in the pathology of septic shockis presently uncertain.

There is also evidence that some of these mediators may act indirectlyvia release of secondary mediators. Thus, the finding that anti-TNFantibodies have little or no protective effect when given after ETexposure⁷ suggests that TNF stimulates the production of another factorthat is the actual hypotensive agent. Once initiated, synthesis andrelease of that factor can apparently continue even in the absence ofdetectable TNF. In 1980, Furchgott et al. (1980)¹⁰ demonstrated thatendothelial cells, which line blood vessels, can be stimulated torelease a substance which relaxes vascular smooth muscle (i.e., causesvasodilatation). Since the chemical nature of this substance wascompletely unknown, it was simply named endothelium-derived relaxingfactor (EDRF). It is hypothesized that many naturally-occurringsubstances which act as physiological vasodilators mediate all or partof their action by stimulating release of EDRF; these substancesinclude, acetylcholine, histamine, bradykinin, leukotrienes, ADP, ATP,substance P, serotonin, thrombin and others.

The extremely short lifetime of EDRF (several seconds) hampered earlyefforts to chemically identify this molecule. In 1987, severallaboratories suggested that EDRF may be nitric oxide (NO), whichspontaneously decomposes to nitrate and nitrite. However, thefundamental problem in accepting this NO hypothesis was that mammaliansystems were not known to contain an enzymatic pathway which couldsynthesize NO; additionally, a likely precursor for NO biosynthesis wasunknown.

After observing that the arginine analog L-N^(G) -methylarginine (L-NMA)could inhibit vascular EDRF/NO synthesis induced by acetylcholine andhistamine, and that EDRF/NO synthesis could be restored by adding excessL-arginine, certain of the present inventors proposed that arginine isthe physiological precursor of EDRF/NO biosynthesis¹¹. Certain of thepresent inventors later demonstrated that inhibition of EDRF/NOsynthesis in the anesthetized guinea pig raises blood pressure.

The enzyme responsible for NO synthesis (nitric oxide synthase) has beenpartially characterized by some of the present inventors¹⁴ and acts tooxidize a terminal nitrogen of the quanidino group of arginine,resulting in production of nitric oxide and citrulline.Macrophage-derived nitric oxide is now considered an importanttumoricidal and bactericidal agent.

It has been reported that macrophage cells become "activated" by 12-36hour after treatment with gamma-interferon, bacterial endotoxin andvarious cytokines in vitro. However, this in vitro "activation" systemhad been associated only with the initiation of tumor cell killing.

However, none of the literature or studies available prior to thepresent inventors work associated hypotension with nitric oxide, or theinvolvement of macrophages with hypotension.

Macrophages are a quantitatively insignificant component of normal bloodvessel walls, and have never been shown to play any role in bloodpressure regulation; i.e., there existed no biochemical, physiologicalor immunological data to suggest that macrophages had any role inpathological hypotension. Thus, the inventors sought to investigate therole of nitric oxide in systems relevant to the manifestation ofhypotension, specifically the role of cytokine induced pathologicalhypotension, particularly on cells which comprise blood vessel walls.

Cytokines are well known to cause morphological and functionalalterations in endothelial cells described as "endothelial cellactivation". Distinct immune-mediators such as tumor necrosis factor(TNF), interleukin-1 (IL-1), and gamma-interferon (IFN) appear to inducedifferent, but partially overlapping, patterns of endothelial cellactivation including increased procoagulant activity¹⁶, PGI2production¹⁷, HLA antigen-expression¹⁸ and lymphocyte adhesion moleculeactivation. Although these cytokines are reported to cause hypotension,vascular hemorrhage, and ischemia, the underlying mechanisms of alteredvasoactivity are unclear¹⁹,20.

In both clinical and animal studies on the effects of biologicalresponse modifiers²¹,22, a major dose limiting toxicity has beenhypotension and vascular leakage. The inventors have observed thatendotoxin and tumor necrosis factor can induce over production of nitricoxide in animals.²³,24 Nitric oxide is a vasoactive substance whichcontrols resting blood pressure.¹² This led the present inventors topostulate that hypotension in humans resulting from administration ofbiological response modifiers or from the development of overwhelmingbacterial infections is due to excessive production of nitric oxide insufficient concentration to relax vasoconstriction. However, macrophagesare known to compose quantitatively only an insignificant component ofnormal blood vessel walls. Moreover, as a practical matter, it wasunlikely that the amount of nitric oxide generated by circulatingmacrophages would be sufficient to elicit a "hypotensive" effectphysiologically, as nitric oxide is not produced in vast enoughquantities by the limited number of macrophages in blood vessel walls toproduce such a pronounced physiological response. This, together withthe recognized short half-life nitric oxide in vivo (3-5 seconds),diminished the theory that macrophage-derived nitric oxide was involvedin hypotension.

The inventors also observed that nitric oxide is derived from the aminoacid L-arginine.¹¹,25 L-arginine is a typical ingredient in commerciallyavailable TPN (total parenteral nutrition) formulations.

The inventors postulated that: 1) other cell types were possibly linkedto pathological hypotension, such as those cells associated with bloodvessel walls (endothelial cells); 2) vascular (e.g., endothelial) cellsmay be stimulated to produce NO by stimuli similar to those stimulifound to trigger NO generation by macrophage; and 3) septic shock (i.e.,systemic vasodilatation induced by bacterial endotoxin) may result frommassive activation of NO biosynthesis by cells which are aquantitatively significant component of normal blood vessel walls.

As hypotension has been observed in patients maintained on standard TPNformulations, a potential valuable improvement in managing the risk ofhypotension in these TPN-receiving patients is postulated by theinventors to be provided through a modified TPN formulation whichreduces or eliminates the potential synthesis of nitric oxide. As thepresent inventors have observed that nitric oxide is derived from theamino acid arginine, the modification of a TPN formulation to reduce oreliminate the availability of arginine will reduce the production ofnitric oxide and the hypotensive effects nitric oxide causes in patientsreceiving or producing endotoxin, or receiving tumor necrosis factor, orany other of a variety of biological response modifiers.

A TPN regimen of low or essentially arginine-free formulations isproposed by the inventors to reduce, if not eliminate, the risk ofhypotension and septic shock in patients with bacterial infections.Clinical regimens which typically require the administration of a TPNformulation include, for example, nutritional support of cancer patientsand others who have no or limited ability to tolerate oral feeding.

SUMMARY OF THE INVENTION

The present invention relates to methods and formulations for preventingor inhibiting systemic hypotension in an animal induced by a biologicalresponse modifier or by bacterial sepsis. By way of example, thebiological response modifiers which are linked to causing systematichypotension include the cytokines IFN, TNF, IL-1 and IL-2. The claimedmethod involves administering, preferably parenterally, an amount of aformulation which is arginine-free to a hypotensial or potentiallyhypotensive animal to reduce the level of serum arginine systemically,and thereby effect a reduction in the synthesis of nitric oxide.

The inventors have observed that nitric oxide is derived from the aminoacid L-arginine. Therefore, the methods of the present invention includeformulations having only very low concentrations of arginine or whichare essentially arginine-free. Reduced arginine will serve to reducenitric oxide synthesis and thus reduce the systemic hypotension manifestin an animal with an elevated levels of nitric oxide.

Particular embodiments of the TPN anti-hypotensive formulations includethe addition of citrulline and/or ornithine. Citrulline and/orornithine, which do not directly result in nitric oxide production, maybe included to satisfy metabolic requirements such as those of the ureacycle, for example. As used in the present application, the term "low"arginine refers to a TPN solution which includes less than 0.1% argininein the feeding solution (<100 mg. arginine/100 ml TPN). An even morepreferred embodiment of the formulation includes a concentration ofarginine between 0.1% and 0.001% arginine. Even more preferably, theanti-hypotensive TPN of the present invention includes about 0.001% (1mg/100 ml TPN) arginine. In a most preferred embodiment of the presentmethods and formulations, arginine is included in the formulation attrace amounts of less than 0.1 mg/100 ml (about 0.0001%). Theformulation in its most preferred embodiment is essentiallyarginine-free.

In a most preferred embodiment of the described methods, the formulationemployed is an essentially arginine-free formulation and is alsoessentially ornithine-free and citrulline free. Alternatively, theessentially arginine-free formulation may include ornithine orcitrulline. So formulated, the present methods also provide a speciallytailored total parenteral nutrition (TPN) formulation for a patient atrisk of systemic sepsis or suffering from other nitric oxide-mediatedhypotension.

Although administration of the formulation to an animal is preferablyparenteral, it is contemplated that other administration routes, such asby oral administration, for example, may prove useful as the method bywhich the essentially arginine-free or low arginine formulations may beused in the claimed method for inhibiting or preventing hypotension.

In one embodiment of the method, the arginine-free formulation isadministered to an animal which may develop, is possibly developing, oris experiencing NO-mediated systemic hypotension. The arginine-freeformulations of the present inventive methods preferably include anypharmaceutically acceptable addition salts as commensurate with plannedtreatments.

A particular preferred use of the method of the present invention is inthe prophylaxis or treatment of systemic hypotension manifest in apatient receiving chemotherapeutic agents, such as TNF, IL-2(interleukin-2), IL-1 (interleukin-1), or a combination thereof. In thisrespect, the method involves administering to the patient, anutritionally supportive amount of a low arginine or essentiallyarginine-free amino acid TPN formulation for a period of time until anelevation in the animal's systolic blood pressure to a physiologicallyacceptable level is demonstrated. By way of example, a physiologicallyacceptable systolic blood pressure level in an adult human is 100 mm Hg(100 millimeters of mercury) or greater. An adult human having asystolic blood pressure level of less than 100 mm Hg is defined asmanifesting the condition known as "hypotension" for purposes of themethods of treatment defined herein. Most preferably, the formulation isprepared so as to be suitable for administration as a parenteralformulation to a patient.

An additional important application of the present invention is as amethod for the treatment of septic shock, particularly that septic shockinduced by bacterial endotoxin. Although prophylaxis is not practicalhere, treatment to improve and eliminate the condition is essential. Thepreferred method of treatment of septic shock according to the presentinvention therefore comprises maintaining the patient on anarginine-free or low arginine formulation comprising a mixture of aminoacids until the patient demonstrates a maintained systolic bloodpressure within physiologically acceptable levels. In an adult human, aphysiologically acceptable systolic blood pressure is at least about 100mm Hg (100 millimeters of mercury). Most preferably, the formulation isprepared so as to be suitable for administration as a parenteralformulation, and thus must be of a physiologically acceptable pH foradministration parenterally.

Septic shock is a life-threatening condition that results from exposureto bacterial endotoxin. It is manifested by cardiovascular collapse andmediated by the release of cytokines such as for example TNF or IL-1.³⁶The inventors have found that the administration of 40 μg/kg ofbacterial endotoxin to dogs causes a 33% decrease in peripheral vascularresistance and a 54% fall in mean arterial blood pressure within 30 to90 minutes. The inventors demonstrated a normalization of vascularresistance and systemic arterial pressure in a hypotensive animal within1.5 minutes after intravenous administration of N^(G) -methyl-L-arginine(20 mg/kg). N^(G) -methyl-L-arginine is a potent and selective inhibitorof nitric oxide synthesis. Although N^(G) -methyl-L-arginine injectionalso increased blood pressure in control dogs, the hypertensive effectwas much greater in endotoxemic dogs (24.8±4.7 mm Hg vs 47.8±6.8 mm Hg,n=4). N^(G) -methyl-L-arginine caused only a modest increase in bloodpressure in control dogs made hypotensive by continuous intravenousinfusion of nitroglycerin (17.1±5.0 mm Hg, n=3).

From these observations, the inventors propose, for the first time, amethod for providing nutritional support and treating an animalincluding humans, in septic shock, at risk of developing septic shock,or having hypotension in a total parenteral formulation (TPN) which isessentially arginine-free. The inventors' observations reported hereinregarding the correlation between serum arginine levels and bloodpressure (See Examples 1 and 2), led to the development of a regimen ofan essentially arginine-free or anti-hypotensive concentration ofarginine in a mixture of amino acids in a formulation which may increaselife-threatening, low blood pressure levels to physiological acceptablelevels. A reduction in serum arginine blood levels through theadministration of such a formulation, thus reducing nitric oxidesynthesis in vivo, is predicted by the inventors to provide an effectivemethod of treating systemic shock and hypotension in an animal,including humans.

The inventors data also provides a proposed method by which hypotensionmay be inhibited or prevented by administering to a patient susceptibleor at risk of developing hypotension, a formulation which is low inarginine (an anti-hypotensive concentration of arginine) or isessentially arginine-free. For purposes of the present application, a"low" concentration of arginine (an anti-hypotensive concentration ofarginine) in the parenteral formation comprises less than 100 mgarginine/100 ml of formulation (0.1%). Even more preferably, a lowconcentration or an anti-hypotensive concentration of arginine comprisesless than 0.0% arginine (10 mg/100 ml) of formulation. Still anotherpreferred embodiment of the inventive method provides a formulationwhich includes 0.001% (or 1 mg/100 ml) or less arginine. Mostpreferably, the parenteral formulation includes 0.0001% arginine (0.1mg/100 ml) or less.

Most preferably, this formulation is parenterally administered. Inanother embodiment, the formulation includes ornithine or citrulline inconcentrations sufficient to meet physiological needs, such as urea acidcycle substrate requirements, of the patient where the parenteralformulation comprises the total nutritional support of the patient. Theformulation should also be adjusted so as to be physiologicallycompatible for parenteral administration, such as to adjust the pH ofthe solution to be between 7.0 and 7.4.

When the formulation employed in the described method includes ornithineand/or citrulline, those concentrations of ornithine and citrulline mostpreferred to be included as part of the formulation are in the range ofbetween about 1-2 g/l (or 0.10-0.20%) ornithine and/or 1-2 g/l(0.10-0.20%) of citrulline. The ornithine concentration mostparticularly preferred as part of the formulation is between 2-4 g/l ofthe TPN formulation in a patient-ready feeding formulation.

As used in the present application, a patient "at risk" for developinghypotension is defined as a patient who is receiving a regimen, or whois prescribed a regimen, of immunomodulators, such as, for example,tumor necrosis factor or interleukin-1 or -2, or who is suffering fromsystemic hypotension. Other patients at risk include patients withoverwhelming bacterial infections or whom have been exposed to abacterial endotoxin.

According to the presently disclosed methods for preventing hypotensionin a patient, a patient would first be identified as "at risk" ofhypotension. The identified person would then be administered alow-arginine or essentially arginine-free formulation which includes amixture of amino acids in nutritionally supportive concentrations.Nutritionally supportive concentrations of amino acids as includedwithin a parenteral formulation are provided at Table 3. The mixture ofamino acids is ornithine-free and citrulline-free in one particularlypreferred embodiment.

In still another embodiment of the present invention, the mixture ofamino acids includes ornithine and citrulline in a concentrationsufficient to meet physiological urea acid cycle substrate requirementsof the patient. The formulation would be administered to the patientuntil a systolic blood pressure of physiologically acceptable levels isobserved in the patient.

The "low" concentrations of arginine as defined for the presentinvention is between 0.001% and 0.1% arginine in a formulation ready tobe administered to a patient (i.e. "patient ready"). The most preferredmode of administering the formulation to a patient is parenteral.Therefore, the most preferred embodiment of the described treatmentformulation may be described as a total parenteral nutrition (TPN)formulation.

A mixture of particular essential and non-essential amino acids areincluded in the claimed anti-hypotensive formulations. A classificationof amino acids recognized by those of skill in the art as "essential" or"non-essential" is provided in Lehninger et al.'s Biochemistry text,²⁶and in Wagner²⁷. These references are specifically incorporated hereinby reference for this purpose.

Arginine is typically included in previously employed parenteralformulations commercially available. The concentration of arginine instandard formulations is about or greater than 0.4%. The presentapplication presents a novel method of preventing/controlling/inhibitinghypotension and treating septic shock through the limitation and/orexclusion of arginine as an ingredient in a TPN formulation. Forexample, the claimed formulations include in one particular embodiment,less than 0.1% arginine in a patient-ready formulation. The mostpreferred embodiment of the present invention employs an essentiallyarginine-free formulation which is also essentially ornithine-free andcitrulline-free.

The involvement of arginine in hypotension and septic shock isdemonstrated in the in vivo studies described herein. Studies conductedby the inventors also demonstrated that particular analogs of arginine(arginine antagonists) inhibit hypotension in vivo. The administrationof particular arginine analog antagonists was thus found by theinventors to affect a variety of biochemical pathways physiologically,most notably by decreasing the production of nitric oxide.

The production of nitric oxide is proposed by the present inventors tobe controllable through the limitation or elimination of available serumarginine in an animal. This goal of limiting or eliminating arginine inanimal serum sufficient to reduce nitric oxide synthesis may mostconveniently be accomplished through maintaining the animal on anarginine-free or low arginine nutritional regimen.

Because arginine is a typical ingredient in standard parenteralformulations and contributes as a urea cycle substrate, the parenteralformulation employed in the claimed methods in particular embodiments ofthe invention may include ornithine or citrulline. Ornithine andcitrulline are known not to be direct precursors of NO, and are expectednot to enhance or contribute to nitric oxide production or maintenanceof nitric oxide levels. Ornithine or citrulline thus may be included asan effective urea cycle substrate to maintain physiological balance inthe animal.

In a more general sense, the present invention may relate to a methodfor the prophylaxis or treatment of nitric oxide-induced systemichypotension in a patient requiring total parenteral nutritional support.The necessity for maintaining a patient on a parenteral nutritionalregimen occurs when a patient is unable to swallow, such as is typicalof patients receiving chemotherapeutic agents which induce nausea,emesis or anorexia.

The arginine-free formulation is to be administered on an "as needed"basis, as determined by the attending physician until a sustainedsystolic blood pressure of at least 100 mm Hg is detectable in thepatient. More specifically, and by way of example, the patient'ssystolic blood pressure should be monitored periodically until asystolic blood pressure of at least 100 mm Hg is recorded over at leasta single 24 hour period.

While not intending to be limited to any particular theory or mechanismof action, it is postulated that the administration of an essentiallyarginine-free parenteral formulation will inhibit hypotension becausesuch a reduction in serum-arginine levels will elicit a reduction innitric oxide synthesis. Nitric oxide, as already discussed, has beenobserved by the inventors to constitute the vasoactive substance whichcauses hypotension in animals receiving biological response modifiers orendotoxin which causes septic shock. This theory is drawn from theinventors observations that patients receiving tumor necrosis factoralso exhibit elevated blood nitric levels (a stable breakdown product ofnitric oxide) when hypotension is manifest.

Arginine has been described as important in the urea cycle, and is thusimportant in overall patient health and disease. Therefore, aformulation with low or no arginine may be supplemented to maintain theoverall health of the patient by including other nutritionally valuableingredients. By way of example, the formulation may be supplemented bythe inclusion of such nutritionally valuable ingredients as ornithine orcitrulline, or both. Both ornithine and citrulline may be converted toarginine in the liver, and thus adequately sustain the urea cycle in apatient maintained on such formulation. Employing these methods andformulations, those persons who may have already lapsed into a state ofseptic shock, or who are already severely ill and being maintained on arespirator with total parenteral nutritional support, may benutritionally supported without increasing the risk of exacerbating analready existing condition of septic shock or hypotension.

For purposes of the present inventive formulations and methods, the term"essentially arginine free" is defined as a final concentration ofarginine of less than 0.0001% arginine by weight. A total volume ofready to feed TPN may be prepared by mixing 500 cc of a 2× concentrateof amino acids together with 500 cc of dextrose solution, mostpreferably containing minerals and vitamins.

Within this specification, the acronym "NO" will be understood torepresent nitric oxide as well as any other additional vasoactivenitrogen oxides. Other abbreviations used in the drawings and otherplaces in this application include the following.

ACh=acetylcholine

BAEC=bovine aortic endothelial cells

B.P.=blood pressure

CO=Cardiac output

EDRF=Endothelium-Derived Relaxing Factor

ET=endotoxin

GP=guinea pig

HIST=histamine

IFN=gamma-interferon

IV=Intravenous

L-Arg=L-arginine

LPS=lipopolysaccharide (endotoxin)

MBEC=murine brain endothelial cells

NO=Nitric Oxide

PAF=Platelet Activating Factor

PPS=Platelet--poor, plasma-derived serum

SAP=Systemic arterial pressure

SNP=sodium nitroprusside

SVR=Systemic vascular resistance

TNF=Tumor Necrosis Factor

TPN=Total Parenteral Formulation

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Clinical studies of biologic response modifiers such as certaincytokines have shown that a major dose-limiting toxicity associated withadministration of such agents is hypotension. Nitrite, the predominantspontaneous oxidation product of NO, is readily assayed and used hereinfor assays of NO production. Nitric oxide (NO) is a highly reactivecompound which spontaneously decomposes to nitrate and nitrite in aculture medium.

The present invention involves implements the inventors' findings thatIFN (100 U/ml) in combination with either TNF (500 U/ml), IL-1 (10U/ml), or endotoxin (1 μg/ml.), can induce MBEC's to accumulate nitritein a culture medium (15 to 80 μM) within 48 hours. TNF, IL-1 orendotoxin alone was found to induce the production of minimal levels ofnitrites (1-3 μM).

The release of vasoactive factors such as NO by endothelial cells mayplay a role in the development of hypotension associated with theadministration of these agents in vivo. This invention relates to ademonstration that cultured MBEC's produce NO in response to variouscombinations of cytokines and the potential role of NO in thepathophysiological causes of hypotension and cardiovascular collapse.

The present invention also relates to a method for inhibiting orpreventing hypotension as well as septic shock through the reduction ofnitric oxide synthesis. Most particularly, the method employs theadministration of an arginine-free parenteral formulation to effect areduction in serum arginine levels. This reduction in serum argininelevels is postulated to provide for a reduction in nitric oxidesynthesis, as arginine is the substrate from which nitric oxide isformed. Nitric oxide has recently been demonstrated by the inventors tobe derived from the amino acid L-arginine.¹⁵

As nitric oxide is a potent vasodilator linked to the development ofhypotension and septic shock, the claimed methods propose the inhibitionand prophylaxis of these conditions in an animal through the control ofserum arginine concentrations and nitric oxide synthesis. The inventionprovides a reduction in nitric oxide synthesis by eliminating orlimiting the arginine concentration in an animal's serum. A reduction inan animal's serum concentration of arginine is accomplished throughrestricting the amount of arginine given to the animal to not greaterthan about 0.1% arginine in a non-hypotensive TPN formulation.

Particular embodiments of the claimed formulations may include ornithineand citrulline, ornithine alone, or citrulline alone to supplement ureacycle substrate physiological requirements in the animal.

The present inventors have found that increased concentrations ofnitrites were not associated with MBEC exposed to TNF and IFN inarginine-free culture medium. The nitrite concentration was found toincrease in a dose dependent manner upon addition of L-arginine back tothe medium of a culture of MBEC cells. The inventors have also foundthat nitrite accumulates when cultured mouse endothelial cells areexposed to immunomodulators and endotoxin¹⁷.

For purposes of the present invention, the term "cytostatic" is definedas that physiological state of a cell characterized by a lack of activecell division. Thus, a culture or group of cells which are in a"cytostatic" state are not actively dividing or which are growthinhibited (i.e., virtually no cell growth).

The terms "anti-hypotensive" and "non-hypotensive" are usedinterchangeably in defining the present invention. These terms areintended to denote the nature of the formulation as limiting the onsetof hypotension through decreased arginine concentrations and thusavailability in the serum of arginine.

For purposes of the present invention, a "pressor" agent is defined as apharmacological agent which causes an increase in blood pressure whenadministered to an animal. By way of example, phenylephrine is a"pressor" agent. However, other pressor agents would be expected toprovide similar effects in the systems described herein. Other examplesof pressor agents include dopamine, epinephrine, norepinephrine andphenylephrine.

The following examples are presented to describe the best mode,preferred embodiments and utilities of the present invention and are notmeant to limit the present invention unless otherwise stated in theclaims appended hereto. The following examples detail particular aspectsand embodiments of the present invention:

EXAMPLE 1--Correlation Between Serum Arginine Levels And Blood Pressure

EXAMPLE 2--Correlation Between Plasma Arginine Levels And Response ToPressor Agents

EXAMPLE 3--Anti-Hypotensive Arginine-free TPN formulation

EXAMPLE 4--Anti-Hypotensive Formulation with Low Arginine

EXAMPLE 5--Anti-Hypotensive Arginine-Free TPN Formulation

PROPHETIC EXAMPLE 6--Formulations and Methods for Inhibiting Hypotensionand Septic Shock

EXAMPLE 1 Correlation Between Serum Arginine Levels and Blood Pressure

The present example is provided to demonstrate the correlation betweenplasma arginine levels and blood pressure. More specifically, thepresent example demonstrates a correlation between low plasma argininelevels and increased blood pressure in endotoxin-treated animals.

The present example also demonstrates the utility for employing aparenteral formulation which is essentially arginine free or low enoughin arginine to lower plasma arginine levels, to prevent or alleviatesynthesis of nitric oxide. The onset of life-threatening levels of lowblood pressure, such as that typically attendant to hypotension andseptic shock would thus be prevented or alleviated in an animal.

The enzyme arginase was used to reduce plasma arginine levels inSpraque-Dawly rats (Weight per rat=250-300 gm). Arginase is an enzymethat irreversibly converts L-arginine to L-ornithine+urea. The rats wereanesthetized with ethyl ether and then pithed as described Shiply andTilden³⁰. The animals were pithed prior to use in the present study soas to eliminate any neurological control of blood pressure.

Arginase was dissolved in sterile saline (1000 I.U./ml) and wasadministered by intravenous infusion at a rate of 300 I.U./min. for 20min. One I.U. is the amount of arginase that converts 1 μmol of arginineto products per minute. Blood pressure was determined using a pressuretransducer connected to an indwelling catheter placed in the carotidartery as described.¹²

Serum arginine concentrations

The administration of arginase to pithed rats with or without exposureto endotoxin (15 mg/kg dose, ip), according to the dose outlined above,resulted in a decrease in plasma arginine levels of from 150 μM to ≦4 μMwithin a few minutes. Plasma arginine remained at levels ≦4 μM for atleast 1 hour after the arginase infusion was stopped.

Blood pressure recording in the pithed rat.

To record blood pressure, a tracheotomy was first performed on each rat,after which the rats were artificially respired with room air. The leftcommon carotid artery was then cannulated in each rat for blood pressuremeasurement via a Statham pressure transducer (Hato Rey, Puerto Rico)and displayed on a physiogram (Grass Instruments, Qunicy Mass.). Heartrate was measured from the lead III electrocardiogram.

Two separate groups of animals were examined. The first group ofanimals, designated the "control" group, received no endotoxin. Theblood pressure of the "control" group animals was measured at twodifferent times, once before the administration of arginase and onceafter the administration of arginase.

The second group of animals, designated the endotoxin group, received asingle dose of endotoxin of 15 mg/kg body weight, which was administeredat least 6 hours prior to any subsequent arginase treatment. The bloodpressure of all animals in both treatment groups was then measured attwo different times, again once before arginase treatment and once afterarginase treatment.

The results from this example are presented in Table 1.

                  TABLE 1                                                         ______________________________________                                        EFFECT OF REDUCED PLASMA ARGINASE                                             ON BLOOD PRESSURE                                                                     No Arginase      Arginase                                                     B.P. (mm Hg)                                                                            Average B.P.                                                                             B.P. (mm Hg)                                     ______________________________________                                        Control                                                                       Rats                                                                          1         61          59.8 ± 1.3                                                                            61                                           2         60                     60                                           3         60                     64                                           4         58                     68                                           Endotoxin Rats                                                                (15 mg/Kg)                                                                    1         36          33.2 ± 3.3                                                                            44                                           2         34                     40                                           3         28                     28                                           4         32                     36                                           5         36                     44                                           ______________________________________                                    

Blood pressure readings for 4 control pithed rats were 61, 60, 60, and58 mm Hg (average 59.8±1.3 mm Hg) (See Table 1). Followingadministration of arginase, blood pressure was unchanged in two rats andincreased by 4 and 10 mm Hg in 2 other rats (average increase 3.5±4.7 mmHg, not statistically significant).

Blood pressure readings for 5 rats at 6 hours after giving 15 mg/kglipopolysaccharide (endotoxin) by intravenous injection was 36, 34, 28,32, and 36 mm Hg (average 33.2±3.3 mm Hg, See Table 1). Note that theendotoxin-treated rats were clearly hypotensive relative to thecontrols.

Following administration of arginase, blood pressure in theendotoxin-treated rats increased by 8, 6, 0, 4, and 8 mm Hg (averageincrease 5.2±3.3 mm Hg). The average blood pressure increase followingarginase treatment of the endotoxic, pithed rats was 15.7%(statistically significant, p<0.05).

Overall, this study shows that reducing plasma arginine levels has nosignificant effect on blood pressure in control animals, but did have asignificant effect on blood pressure readings in endotoxic animals. Thelack of a demonstrated effect in control animals may be due to the slowrate of NO formation in control animals, so as to negate any requirementfor exogenous (i.e. plasma) arginine. Thus, a reduction in plasmaarginine levels in such animals would not be a limiting factor forgenerating NO.

In contrast, the rate of NO formation in endotoxic animals is muchfaster than in control (non-endotoxic animals), and results in thedevelopment of hypotension. In these endotoxic animals, the cells makingNO must obtain extra arginine from the plasma. When plasma arginine isvery low in endotoxic animals (i.e. after arginase administration),there is not enough arginine available to sustain a pathologically highrate of NO synthesis by cells associated with blood vessel walls (i.e.,endothelial cells). Thus, the concentration of NO is reduced, resultingin a concomitant reduction in the level of blood pressure reduction inthe vasculature of the animal. Thus, depletion of serum arginine levelscould be used to effect an increase in blood pressure in hypotensiveanimals.

Thus, use of arginine-free TPN solutions, or solutions sufficiently lowin arginine concentration so as to effect a sufficient reduction inplasma arginine levels adequate to limit nitric oxide synthesis, forexample, to about 4 μM arginine or less (i.e., 4 nM/ml serum arginine),are expected to have a beneficial effect comparable to that of arginaseadministration for preventing or treating hypotension, particularlyhypotension in animals in septic shock.

EXAMPLE 2 Correlation between Plasma Arginine Levels and Response toPressor Agents

The present example is provided to demonstrate the correlation betweenlow plasma arginine levels and increased response to "pressor" agents invivo in endotoxin-treated animals. The particular "pressor" agentemployed in this example is phenylephrine. However, virtually any"pressor" agent could be employed with equal utility to demonstrate thephysiological effects disclosed by the present inventors. It haspreviously been observed that in septic shock, patients are hypotensiveand no longer respond well to the usual pressor drugs such asphenylephrine. To determine if lowering plasma arginine would improveresponsiveness, a second study was carried out in pithed rats.

Animals were pithed as described in Example 1. Blood pressuremeasurements were obtained also as described in Example 1. Arginase wasalso prepared according to the method described in Example 1.

Both left and right Jugular veins were cannulated for drugadministration; and left Jugular was used for bolus administration ofphenylephrine and the right jugular vein was used for continuousinfusion of arginase. All animals from both groups (Control andEndotoxin) received phenylephrine in sequential doses of 0.3, 1.0, 2.0,or 6.0 ug/Kg.

The results from this example are presented in Table 2.

                                      TABLE 2                                     __________________________________________________________________________    EFFECT OF ARGINASE AND ENDOTOXIN ON BLOOD PRESSURE                                           Blood Pressure Increase (mm Hg)                                               Without Arginase With Arginase                                 Phenylephrine dose                                                                           Raw Data  Ave. ± S.D.                                                                       Raw Data  Ave. ± S.D.                      __________________________________________________________________________    Study #1: Control Animals                                                     0.3 μg/Kg   +16, 14, 32, 9                                                                          17.8 ± 5.0                                                                        +4, 9, 20, 10                                                                           13.3 ± 2.5                       1.0 μg/Kg   +40, 25, 36, 24                                                                         31.3 ± 4.0                                                                        +12, 17, 40, 21                                                                         22.5 ± 6.1                       2.0 μg/Kg   +64, 48, 58, 34                                                                         51.0 ± 6.6                                                                        +28, 30, 66, 31                                                                         38.8 ± 9.1                       6.0 μg/Kg   +84, 92, 122, 74                                                                         93.0 ± 10.3                                                                      +64, 72, 120, 63                                                                         79.8 ± 13.4                     Study #2: Endotoxic Animals                                                   0.3 μg/Kg   +2, 0, 4, 2, 3                                                                           2.2 ± 0.7                                                                        +2, 0, 4, 2, 2                                                                           2.0 ± 0.6                       1.0 μg/Kg   +6, 4, 9, 10, 6                                                                          7.0 ± 1.1                                                                        +8, 6, 16, 9, 6                                                                          9.0 ± 1.8                       2.0 μg/Kg   +12, 10, 24, 12, 10                                                                     13.6 ± 2.6                                                                        +19, 14, 44, 20, 20                                                                     23.3 ± 5.3                       6.0 μg/Kg   +25, 26, 72, 26, 20                                                                     33.7 ± 9.6                                                                        +36, 46, 79, 44, 38                                                                     48.5 ± 7.6                       __________________________________________________________________________

This example shows the effects of endotoxin and of arginase on meansystolic blood pressure response to phenylephrine in pithed rats.Endotoxin (15 mg/kg body weight) was given by intravenous injection 6hrs before the experiment began; arginase (300 I.U./Min. for 20 min.)was given intravenously to each rat after the "Without Arginase"measurements were made.

Table 2 shows the maximum increase in blood pressure following thephenylephrine dose indicated for each rat ("Raw Data"); note that thedata is in pairs since each rat was tested first without arginase (at0.3, 1.0, 2.0 and 6.0 ug/Kg phenylephrine, in sequence) and was thenretested with phenylephrine in the same dose and sequence after arginasetreatment. Thus, the first line of data in the Table shows that fourcontrol rats were each tested with 0.3 μg/Kg of phenylephrine. The firstcontrol rat showed a blood pressure of 16 mm Hg without arginase, butonly 4 mm Hg after arginase administration ("with arginase"). For thesecond, third and fourth rats, the blood pressure increments were 14, 32and 9 before arginase, respectively, and 9, 20 and 10 after arginase,respectively.

This data demonstrates that reducing plasma arginine levels througharginase treatment, enhances the "pressor" agent (such asphenylephrine), response in endotoxic animals, reducing the differenceobserved between endotoxic and control animal blood pressure increasesat the same pressor agent dose. Moreover, endotoxic animals pretreatedwith arginase demonstrated an enhanced "pressor" effect (a statisticallygreater increase in blood pressure), compared to the pressor responseobserved in endotoxic animals receiving no arginase (See Table 2).

Endotoxin decreases an animals ability to present the normalhypertensive response (i.e., increase in blood pressure) tophenylephrine. Thus, compare the "Without Arginase" data of control andendotoxic rats at each dose of phenylephrine (Table 2). This effectoccurs because the endotoxic animals are making large amounts of nitricoxide from arginine, and that causes hypotension and blunting of theresponse to phenylephrine.

Arginase administration improves the hypertensive response to a pressoragent, such as phenylephrine, dose. Smaller differences were observedbetween control and endotoxic animals given arginase (indicating only asmall loss of responsiveness) relative to the larger differences betweencontrol and endotoxic animals not given arginase (indicating a largeloss in responsiveness).

For example, at a phenylephrine dose of 6 μg/Kg, in animals not givenarginase (i.e., having a higher serum arginine concentration), thepressor response to phenylephrine drops from 93.0±10.3 mm Hg (apharmacologically useful pressor agent response) in control animals to33.7±9.6 mm Hg (a poor pressor agent response) in endotoxic animals, adifference in pressor response of 59.3 mm Hg. In contrast, at the samephenylephrine dose in animals given arginase (i.e., decreased serumarginine levels), the pressor response in control and endotoxic animalswas 79.8±13.4 and 48.5±7.6, respectively, a difference of only 31.3 mmHg. Thus, depletion of plasma arginine with arginase very significantlyrestores the "normal" (hypertensive) response to pressor drugs, such asphenylephrine.

The data herein thus demonstrates that hypotension may be controlled,particularly in endotoxic animals, by manipulating an animal's serumarginine concentration. As serum arginine levels may be controlled inpart through an animal's nutrition as they are through arginaseadministration, the present data provides a mechanism wherebyhypotension (low blood pressure) may be corrected by maintaining theanimal on a low/anti-hypotensive concentration or essentiallyarginine-free nutritional regimen. As such, the presently disclosedtechnique may also be used to prevent the development of hypotension ina patient at risk.

EXAMPLE 3 Anti-hypotensive Arginine-free TPN formulation

The present example defines an anti-hypotensive TPN formulation of thepresent invention.

A sterile, non-pyrogenic, stable solution for parenteral administrationto a patient having hypotension or at risk of hypotension or systemicshock, particularly those receiving immunomodulatory agents, is preparedfrom pure crystalline amino acids, which are dissolved in a glucosesolution (5% to 20%) in the following concentrations to provide a 2×concentrate TPN or a ready-to-feed TPN formulation, as indicated:

                  TABLE 3                                                         ______________________________________                                                                  Final Concentration                                           2× concentrate                                                                          (Feeding                                            Amino Acids                                                                             mg/100 ml formulation                                                                         Formulation) g/l                                    ______________________________________                                        isoleucine                                                                              600-800         3-4                                                 leucine    800-1200       4-6                                                 valine    600-800         3-4                                                 phenylalanine                                                                           200-400         1-2                                                 methionine                                                                              200-400         1-2                                                 lysine    600-800         3-4                                                 histidine 200-400         1-2                                                 threonine 400-600         2-3                                                 tryptophan                                                                              100-300         0.5-1.5                                             tyrosine   50-150         0.25-0.75                                           alanine    800-1000       4-5                                                 aspartic acid                                                                           400-600         2-3                                                 glycine    800-1000       4-5                                                 proline   600-800         3-4                                                 serine    200-400         1-2                                                 ______________________________________                                    

To obtain the preferred TPN formulation concentration suitable as afeeding formulation, a volume of 500 ml of the 2× concentrate (definedin Table 3) is mixed with 500 ml of a dextrose solution, for theproduction of 1 liter of the feeding formulation (i.e., 500 cc of a 2×concentrate of AA and 500 cc of dextrose solution). Most preferably, thedextrose solution is supplemented with a physiologically acceptableconcentration of vitamins and minerals.

The TPN of the present methods may also include glutamic acid (400-600mg/100 ml of a 2× conc., or 2-3 g/l in a final concentration) and/ortaurine (50-100 mg/100 mls. of a 2-fold concentrate; 0.25-0.5 g/l finalconcentration).

The solution is then filter sterilized into appropriate containers forintravenous fluids. To prepare for administration, the volume is thenbrought to the desired feeding solution concentration with an equalvolume of sterile glucose solution. The TPN as a ready to feedformulation is then to be kept cool. The solution may then beadministered to a patient intravenously (I.V.). The pH of the TPNsolution must also be adjusted to a physiologically acceptable pH,between 7.0 and 7.4. The formulation is arginine free.

EXAMPLE 4 Anti-Hypotensive Formulation with Low Arginine

If a formulation of amino acids for a patient having hypotension, or atrisk of developing hypotension or septic shock, is desired whichincludes arginine, the formulation as outlined in Example 3 may beutilized after supplementation with arginine. Arginine will be added toconstitute less than 0.1% final concentration by weight of theformulation (about 1 g. of arginine/liter of the TPN feedingformulation). The same amounts of the essential and non-essential aminoacids (leucine, isoleucine, valine, phenylalanine, lysine, valine,isoleucine, threonine, tryptophan, histidine, lyrosine, alanine,glycine, proline and serine) as defined in Example 3 will be present;and the solution prepared in the same manner.

EXAMPLE 5 Anti-Hypotensive Arginine-Free TPN Formulation

If a formulation of amino acids for patients at risk of hypotension orseptic shock, or receiving pharmacological agents which may cause such acondition, such as TNF (tumor necrosis factor), etc., is desired whichis essentially arginine-free and contains ornithine and citrulline, theformula as outlined in Example 3 supplemented with ornithine andcitrulline can be utilized.

Ornithine will then be added to constitute between about 1-2 gramsornithine per liter of the TPN feeding solution (between 0.1% and 0.2%by weight ornithine). Citrulline will be added to constitute about 1gram citrulline per liter of the TPN feeding solution (about 0.1% byweight citrulline). The same amounts of the amino acids of Example 3will be present, and the solution prepared in the same manner. Theanti-hypotensive formulation is arginine free.

PROPHETIC EXAMPLE 6 Formulations and Methods for Inhibiting Hypotensionand Septic Shock

The present prophetic example provides methods whereby the particularlydefined arginine-free and low-arginine formulations of Examples 3-5 maybe used in the treatment of patients at risk of developing hypotensionand septic shock, or whom may require parenteral nutritional support andhave already developed hypotension or septic shock.

The proposed formulations and proposed methods may be used mostparticularly in the clinical management of patients requiring totalparenteral nutritional support and receiving immunomodulators. By way ofexample, the term "immunomodulator" refers to such agents as interferon,interleukin-2, and tumor necrosis factor.

Many of the class of substances recognized as immunomodulators are usedas anti-cancer chemotherapeutic agents. Thus, it is envisioned that thepresently described methods would be effective for the clinicalmanagement of patients being maintained on parenteral nutritionalsupport and receiving chemotherapeutic agents with immunomodulatoryaction.

According to the present invention, a method for prophylaxis ortreatment of systemic hypotension related to the elevated production ofnitric oxide in an animal is provided comprising administering to theanimal a non-hypotensive formulation comprising a mixture of amino acidsin a pharmaceutically acceptable diluent. The formulation may beessentially arginine-free, in a most preferred embodiment of the method.A non-hypotensive formulation which includes a low arginineconcentration may also be employed in another embodiment of the claimedmethod.

The formulation is to be administered to the patient until aphysiologically acceptable blood pressure in the animal is reached andmaintained. For a human, a physiologically acceptable systolic bloodpressure level is about 100 mm Hg.

More particularly, the method of the present invention includes anessentially arginine-free or low arginine (between about 0.001% andabout 0.1%) formulation comprising a mixture of amino acids. Theformulation should be prepared so as to be physiologically suitable asan intravenous hyperalimentation (total parenteral nutrition) solutionfor patients requiring such solutions.

Stated as a range of concentrations for the most preferred mixture ofamino acids, the formulation of the presently disclosed methods andspecially tailored arginine-free formulations is defined in Table 4.Most preferably, the proposed concentrations to be included in such aformulation appear in Table 4.

                  TABLE 4                                                         ______________________________________                                        PREPERRED RANGES OF AMINO ACIDS IN                                            NON-HYPOTENSIVE FORMULATIONS                                                  ______________________________________                                        about 3-4 g/l isoleucine (0.3-0.4%);                                          about 4-6 g/l leucine (0.4-0.6%);                                             about 3-4 g/l lysine (0.3-0.4%);                                              about 1-2 g/l methionine (0.1-0.2%);                                          about 1-2 g/l phenylalanine (0.2-0.24);                                       about 2-3 g/l threonine (0.2-0.3%);                                           about 0.5-1.5 g/l tryptophan (0.05-0.15%);                                    about 3-4 g/l valine (0.3-0.4%);                                              about 4-5 g/l alanine (0.4-0.5%);                                             about 1-2 g/l histidine (0.1-0.2%);                                           about 3-4 g/l proline (0.3-0.4%);                                             about 1-2 g/l serine (0.1-0.2%);                                              about 0.25-0.75 g/l tyrosine (0.025-0.075%);                                  about 4-5 g/l glycine (0.4-0.5%); and                                         about 2-3 g/l aspartic acid (0.2-0.3%).                                       ______________________________________                                    

The formulation may also include ornithine. Where ornithine is part ofthe particular formulation, it is to be included at a concentration ofabout 1-2 grams/l of the TPN feeding formulation (about 0.1-0.2%ornithine).

Where the formulation is a parenteral formulation, the mixture should beadjusted so as to be physiologically compatible for parenteraladministration.

The described non-hypotensive parenteral nutritional formulations mayalternatively include low concentrations of arginine found not toprovide sufficient substrate for nitric oxide production in hypotensiveanimals. A low concentration of arginine for purposes of the presentinvention is defined as less than or equal to about 0.1% arginine in thefeeding formulation ready to be administered to the patient. Mostpreferably, the formulation may include between about 0.01% to about0.1% arginine.

An additional most preferred embodiment of the claimed invention isessentially arginine free. In one particularly defined embodiment of theessentially arginine-free formulation, the amino acids ornithine andcitrulline are included. Ornithine and citrulline contribute to the ureacycle substrate requirements of the animal. Where ornithine andcitrulline are included in the formulation, the concentration of theseingredients most preferred comprise about 0.1-0.2% (or 1-2 g/l)ornithine and about 0.1% (or 1 g/l) citrulline.

                  TABLE 5                                                         ______________________________________                                        Arginine-Free Formulation Mixture of Amino Acids                                           2× Concentrate                                                                      Final Feeding                                        Amino Acids  (mg/100 ml) Concentration g/l                                    ______________________________________                                        Isoleucine   600         3                                                    Leucine      1,000       5                                                    Lysine       1,000       5                                                    Methionine   200         1                                                    Phenylalanine                                                                              300         1.5                                                  Threonine    400         2                                                    Tryptophan   200         1                                                    Valine       500         2.5                                                  Alanine      900         4.5                                                  Histidine    300         1.5                                                  Proline      700         3.5                                                  Scrine       400         2.0                                                  Tyrosine     450         2.0                                                  Glycine      800         4.0                                                  Aspartic acid                                                                              600         3                                                    Ornithine    400         2                                                    ______________________________________                                    

The ornithine content described for the formulation above may be omittedand replaced with citrulline at a concentration of about 2 g/l. Theamino acids concentrate (2×0 is mixed with a pharmaceutically acceptablediluent, such as for example, a glucose solution in a proportion of 1 to1 (1 part amino acid solution to 1 part of a dextrose solution). Inaddition, trace elements, vitamin supplements and essential salts (Na⁺,K⁺, PO₄ ⁻ -, Ca⁺⁺, Mg⁺⁺) may be added.

The anti-hypotensive formulations as part of a method for treating orpreventing hypotension may be administered as a parenteral nutritionalformulation according to parenteral feeding methods well known to thoseof skill in the medical arts.

In practicing the claimed method, a physiological benchmark will bereferred to in reference to determining at what point the administrationof the arginine-free formulation should be terminated. For example, thepatient's systolic blood pressure level may be monitored so as todetermine when the patient has reached a physiologically acceptablelevel. A return to normal systolic pressure may then be used to indicatethe point at which nitric oxide production was being reduced, and hadescaped risk of a greater reduction in peripheral vascular resistance orarterial blood pressure.

As generally defined according to the claimed method, hypotension (lowblood pressure) is defined as an adult human systolic blood pressurelevel of less than about 100 mm Hg. A physiologically acceptablesystolic blood pressure in an adult human is at least about 100 mm Hgsystolic blood pressure.⁴⁰

It has been observed that serum arginine levels increase upon theadministration of a standard TPN formulation.⁴¹ Therefore, byeliminating arginine as an ingredient in a TPN formulation, theinventors propose that serum arginine levels will be significantlyreduced in patients receiving such an arginine-free TPN formulation ascompared to similarly situated patients whom had instead been receivinga standard TPN solution. A standard TPN solution which includes greaterthan about 0.1% arginine would not be expected to constitute ahypotensive formulation.

Changes may be made in the following methods and formulations definedtherein, without departing from the scope and spirit of the followingclaims.

Those of skill in the pharmaceutical and/or neurophysiological arts willbe able to practice the present invention with the aid of the disclosureprovided here, the following references may facilitate practice orenhanced understanding of certain aspects. Inclusion of a reference inthis list is not intended to and does not constitute an admission thatthe reference constitutes prior art with respect to the presentinvention.

The following references are specifically incorporated herein byreference in pertinent part for the purposes indicated herein.

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What is claimed is:
 1. An anti-hypotensive parenteral feedingformulation for the treatment of hypotension in an animal consistingessentially of:about 0.001-1 g/l arginine; about 3-4 g/l isoleucine;about 4-6 g/l leucine; about 3-4 g/l lysine; about 1-2 g/l methionine;about 1-2 g/l phenylalanine; about 2-3 g/l threonine; about 0.5-1.5 g/ltryptophan; about 3-4 g/l valine; about 4-5 g/l alanine; about 1-2 g/lhistidine; about 3-4 g/l proline; about 1-2 g/l serine; about 0.25-0.75g/l tyrosine; about 4-5 g/l glycine; and about 2-3 g/l aspartic acid. 2.The anti-hypotensive parenteral formulation of claim 1 further definedas comprising about 1 g/l citrulline.
 3. The anti-hypotensiveformulation of claim 1 defined further as comprising about 1-2 g/lornithine.
 4. A formulation consisting essentially of:about 3-4 g/lisoleucine; about 4-6 g/l leucine; about 3-4 g/l lysine; about 1-2 g/lmethionine; about 1-2 g/l phenylalanine; about 2-3 g/l threonine; about0.5-1.5 g/l tryptophan; about 3-4 g/l valine; about 4-5 g/l alanine;about 1-2 g/l histidine; about 3-4 g/l proline; about 1-2 g/l serine;about 0.25-0.75 g/l tyrosine; about 4-5 g/l ml glycine; about 2-3 g/laspartic acid; and less than about 0.0001% arginine by weight.
 5. Theformulation of claim 4 defined further as including about 1-2 g/lornithine or about 1 g/l citrulline.
 6. A 2× concentrateanti-hypotensive parenteral formulation consisting essentiallyof:600-800 mg/100 ml isoleucine; 800-1200 mg/100 ml leucine; 600-800mg/100 ml valine; 200-400 mg/100 ml phenylalanine; 200-400 mg/100 mlmethionine; 600-800 mg/100 ml lysine; 200-400 mg/100 ml histidine;400-600 mg/100 ml threonine; 10- 300mg/100 ml tryptophan; 50-150 mg/100ml tyrosine; 800-1000 mg/100 ml alanine; 400-600 mg/100 ml asparticacid; 800-1000 mg/100 ml glycine; 600-80 mg/100 ml proline; and 200-400mg/100 ml serinewherein said formulation is arginine-free and inhibitshypotension.